Method and apparatus for performing an in-service upgrade of a switching fabric of a network element

ABSTRACT

A method and apparatus for performing an in-service upgrade of a switching fabric of a network element is described. Network traffic is denominated in cells as it passes through the network element. Prior to the upgrade, an internal header is provided to direct the communication of a cell through the network element. The internal header has internal routing information to direct the routing of the cell through the switching fabric of the network element. Additional internal routing information compatible with upgraded components of a network element is added to the cells passing through the network element. The additional internal routing information is dependent on the internal routing information previously provided in the internal header, but differs from the internal routing information in that it supports the upgraded components of the network element. Thus, prior to the upgrading of a switching fabric in a network element, the internal routing information is used to route the cells through the non-upgraded network components, while, after the upgrading of the switching fabric, the additional internal routing information is used to route cells through the upgraded components of the network element.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/325,341, filed Sept. 27, 2001.

FIELD OF THE DISCLOSURE

The invention relates to network elements in a communication networkand, more particularly, to a capability for performing an in-serviceupgrade of a switching fabric in a network element.

BACKGROUND

In a communication network, a network element is involved in directingnetwork traffic toward its intended destination. Since network trafficcan be very dynamic, the environment within a network element istypically also very dynamic. For example, at various times during theoperation of the network element, new connections are established,existing connections are maintained, and old connections are released.Occasionally, it is desirable to upgrade the switching fabric within thenetwork element. However, it is typically difficult to reconfigure thenetwork element without adversely affecting the network traffic passingthrough the network element. Therefore, some loss of data typicallyoccurs when connections are dropped during an attempt to upgrade anetwork element. Thus, it is desirable to provide the ability to performan in-service upgrade of a switching fabric in a network element withoutloss of data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of a typical cellstructure within a network element.

FIG. 2 is a block diagram illustrating a cell structure in accordancewith an embodiment of the present invention.

FIG. 3 is a block diagram of a switching system in accordance with anembodiment of the present invention in its non-upgraded state as asingle shelf switching system.

FIG. 4 is a block diagram illustrating a switching system in accordancewith an embodiment of the present invention in a partially upgradedstate.

FIG. 5 is a block diagram of a switching system in accordance with anembodiment of the invention in an upgraded state.

FIG. 6 is a block diagram illustrating a line card in accordance with anembodiment of the present invention.

FIG. 7 is a block diagram illustrating a control card in accordance withan embodiment of the present invention.

FIG. 8 is a block diagram of an egress line card capable of supportingredundant switching fabrics in accordance with an embodiment of theinvention.

FIG. 9 is a block diagram illustrating an ingress line card capable ofsupporting redundant switching fabrics in accordance with an embodimentof the invention.

FIG. 10 is a flow diagram illustrating a method for performing anin-service upgrade of a switching fabric of a network element inaccordance with an embodiment of the invention.

FIG. 11 is a flow diagram of a method for performing an in-serviceupgrade of a switching fabric of a network element in accordance with anembodiment of the invention.

FIG. 12 is a flow diagram illustrating a method for backing out of anupgrade process in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE FIGURES

A method and apparatus for performing an in-service upgrade of aswitching fabric of a network element is described. Network traffic isdenominated in cells as it passes through the network element. Prior tothe upgrade, an internal header is provided to direct the communicationof a cell through the network element. The internal header has internalrouting information to direct the routing of the cell through theswitching fabric of the network element. However, if the network elementis being upgraded to a different architecture, for example from a singleshelf architecture to a multiple shelf architecture, the internalrouting information of the internal header may be incompatible with theupgrade components of the network element. Consequently, existingconnections having internal headers with previously determined internalrouting information may be lost when an upgrade is performed. To preventthe loss of connections and consequent loss of data, additional internalrouting information compatible with upgraded components of a networkelement is added to the cells passing through the network element. Theadditional internal routing information is dependent on the internalrouting information previously provided in the internal header, butdiffers from the internal routing information in that it supports theupgraded components of the network element. Thus, prior to the upgradingof a switching fabric in a network element, the internal routinginformation is used to route the cells through the non-upgraded networkcomponents, while, after the upgrading of the switching fabric, theadditional internal routing information is used to route cells throughthe upgraded components of the network element.

The additional internal routing information can be added to cells of newconnections being established, and it can be added to cells of existingconnections. For example, after the commencement of an upgrade process,all new connections can be established such that both the internalrouting information and the additional internal routing information areadded to cells of that connection. Also, a sub process can be performedin which the additional internal routing information is added to cellsof existing connections. Thus, when the network element is ready for theupgrading of the switch fabric, the cells of both new connections andexisting connections will be associated with both internal routinginformation and additional routing information. Thus, those cells can berouted using either the non-upgraded components of the network elementor the upgraded components of the network element.

The ability to switch cells using either the non-upgraded components orthe upgraded components is useful in a network element. For example, anynetwork element having a redundant architecture, in the event thateither the non-upgraded components or the upgraded components were tofail, network traffic could be routed to components of the oppositetype. As an example, if non-upgraded network component handling networktraffic were to fail, the network traffic could be routed through theupgraded component. As another example, if an upgraded componenthandling network traffic were to fail, the network traffic could berouted through a non-upgraded component.

As another example, in the event that a problem were to occur during theupgrade process that would indicate the desirability to back out of theupgrade and revert to the original configuration of the network element,the availability of information to allow routing through either thenon-upgraded components or the upgraded components avoidsincompatibility problems, thereby facilitating a swift transition backto the original configuration of the network element.

FIG. 1 is a block diagram illustrating an example of a typical cellstructure within a network element. The cell structure includes a firstheader 101 and a payload 103. The first header 101 includes internalrouting information compatible with non-upgraded components of thenetwork element. The payload 103 includes user data to be transportedthrough the network element.

FIG. 2 is a block diagram illustrating a cell structure in accordancewith an embodiment of the present invention. The cell structure includesfirst header 201, second header 202, and payload 203. The first header201 includes internal routing information compatible with non-upgradedcomponents of the network element. The second header 202 includesadditional internal routing information compatible with upgradedcomponents of the network element. The payload 203 includes user data tobe transported through either the non-upgraded components or theupgraded components of the network element. First header 201 and secondheader 202 may be formatted as distinct headers, or they may be a singleheader with the space for second header 202 defined within the overallsingle header structure. While the term header is used, it should beunderstood that the first header 201 and second header 202 may be at thehead of a cell, at the tail of a cell, or at any other location withinthe cell relative to payload 203. The first header 201, the secondheader 202, and the payload 203 may be of fixed or variable length. Ifany of the first header 201, second header 202, or payload 203 are ofvariable length, it is important to ensure that they can beunambiguously identified, for example through the use of unique coding.

FIG. 3 is a block diagram of a switching system in accordance with anembodiment of the present invention in its non-upgraded state as asingle shelf switching system. While it is described as a single-shelfswitching system, that description is not intended as a limitation onthe form factor of the switching system but rather to contrast theswitching system with an upgraded switching system. The switching system301 comprises line cards 302 through 305, switching cards 306 and 307,and control card 308. Communication lines 309 through 312 are coupled toline card 302 through 305, respectively. Line cards 302 through 305 arecoupled to switching cards 306 and 307 via coupling 313. Line cards 302through 305 and switching cards 306 and 307 are coupled to control card308 via coupling 314. Line cards 302 through 305 provide an internalheader containing internal routing information to cells passing throughthem. The internal routing information of the internal header iscompatible with switching cards 306 and 307, allowing switching cards306 and 307 to properly switch the cells passing through them. Controlcard 308 provides control of line cards 302 through 305 and switchingcards 306 and 307. In accordance with an embodiment of the invention,switching cards 306 and 307 are replaceable by fabric interface cards(and switching shelves, wherein the fabric interface cards are coupledto the switching shelves). Optionally, at least one of line cards 302through 305 may insert internal routing information into a portion of aninternal header other than a predefined field therein designated foradditional internal routing information.

FIG. 4 is a block diagram illustrating a switching system in accordancewith an embodiment of the present invention in a partially upgradedstate. The switching system 301 includes line cards 302 through 305,switching card 306, fabric interface card 401, and control card 308.Communication lines 309 through 312 are coupled to line cards 302through 305, respectively. Line cards 302 through 305 are coupled toswitching card 306 and fabric interface card 401 via coupling 313.Control card 308 is coupled to line cards 302 through 305, switchingcard 306, and fabric interface card 401 via coupling 314. Fabricinterface card 401 is coupled to switching shelf 402 via coupling 403.

Fabric interface card 401 has been installed in place of switching card307 of FIG. 3. Fabric interface card 401 adapts switching system 301 toutilize the switching fabric of switching shelf 402. However, it is notalways possible or preferable to make upgraded components, such asfabric interface card 401 and switching shelf 402 compatible with theinternal routing information of the internal headers of cells used inswitching systems such as the switching system illustrated in FIG. 3.For example, the internal routing information may provide insufficientcapacity to fully describe the appropriate routing for a cell within thecontext of the expanded routing capability provided by the upgradedcomponents of the network element. Thus, by providing an internal headerhaving both internal routing information compatible with a non-upgradedcomponent, such as switching card 306, and an upgraded component such asfabric interface card 401 and switching shelf 402, either or both ofswitching card 306 and the combination of fabric interface card 401 andswitching shelf 402 may be used to switch any cell passing through thenetwork element. Therefore, if switching card 306 is configured to beredundant with switching shelf 402, any failure of switching card 306can be accommodated by transferring the network traffic to switchingshelf 402, and any failure of switching shelf 402 can be accommodated bytransferring the network traffic to switching card 306.

FIG. 5 is a block diagram of a switching system in accordance with anembodiment of the invention in an upgraded state. Switching system 301includes line cards 302 through 305. Communication lines 309 through 312are coupled to line cards 302 through 305, respectively. Line cards 302through 305 are coupled to fabric interface cards 401 and 501 viacoupling 313. Control card 308 is coupled to line cards 302 through 305and fabric interface cards 401 and 501 via coupling 403. Fabricinterface card 501 is coupled to switching shelf 502 via coupling 503.

Control card 308 programs line cards 302 through 305 to add an internalheader to a payload of the cells passing through switching system 301.The internal header includes both internal routing informationcompatible with non-upgraded components and additional routinginformation compatible with upgraded components. Fabric interface cards401 and 501 pass the cells to switching shelves 402 and 502,respectively. Switching shelves 402 and 502, along with their fabricinterface cards 401 and 501, respectively, are capable of switchingcells in accordance with the additional internal routing informationprovided in their internal headers. Consequently, the internal routinginformation originally provided in the internal header is no longerneeded in the switching system illustrated in FIG. 5. Thus, once theswitching system has been upgraded to the upgraded state illustrated inFIG. 5, the inclusion of the internal routing information originallyprovided in the internal header may be discontinued and the upgradingprocess may be concluded. The space in the internal header previouslyoccupied by the internal routing information may be reserved for futureuse or, if no longer needed, may be eliminated, thereby reducing thesize of the internal header. Control card 308 can program line cards 302through 305 to discontinue the insertion of the internal routinginformation originally provided in the internal header when appropriate.

FIG. 6 is a block diagram illustrating a line card in accordance with anembodiment of the present invention. The line card 601 includes cellmodification circuit 602, processor 603, and optionally, packetprocessing circuit 604, packet processing circuit 605, and headerremoval circuit 606. Cell payloads received by line card 601 anddestined to be switched by the switching fabric of the network elementare received at input 607. Input 607 is coupled to optional packetprocessing block 604 which performs any necessary preprocessing of thecells. Packet processing circuit 604 is coupled via coupling 608 to cellmodification circuit 602. A control input 611 from a control card iscoupled to processor 603. Processor 603 provides a control output 612coupled to cell modification circuit 602 to control the operation ofcell modification circuit 602. Cell modification circuit 602 modifiescells passing through line card 601 in accordance to the programmingprovided to it from processor 603 or, externally, from a control card.Cell modification circuit 602 can be programmed to add an internalheader to the cells which may contain internal routing informationcompatible with non-upgraded components, additional internal routinginformation compatible with upgraded components, or both. Once the cellsare modified, cell modification circuit 602 provides the cells an output609 to packet processing circuit 605. Packet processing circuit 605performs any necessary post processing of the cells. Optional packetprocessing circuit 605 provides output 610 to the switching fabric ofthe network element. Cells are received from the switching fabric of thenetwork element via input 613, which is coupled to header removalcircuit 606. The optional header removal circuit 606 removes theinternal headers from the cells and forwards them to output 614.

FIG. 7 is a block diagram illustrating a control card in accordance withan embodiment of the present invention. Control card 701 includesupgrade controller 702, connection management sub system 703, fabricmanagement subsystem 704, and content messaging subsystem 705. Upgradecontroller 702 is coupled to connection management subsystem 703 viacoupling 706. Upgrade controller 702 is coupled to fabric managementsubsystem 704 via coupling 707. Connection management subsystem 703 iscoupled to content messaging subsystem 705 via coupling 708. Fabricmanagement subsystem 704 is coupled to content messaging subsystem 705via coupling 709. Content messaging subsystem 705 provides controloutput 710, which may be coupled to one or more line cards.

The upgrade controller 702 provides control over the upgrade process andcontrols connection management subsystem 703 and fabric managementsubsystem 704. Connection management subsystem 703 programs line cardsto modify cells to include an internal header. The internal header mayinclude internal routing information. The internal header may alsoinclude either additional internal routing information or a predefinedfield for storing additional internal routing information. Connectionmanagement subsystem 703 can also program line cards to omit informationfrom the internal header, for example, either the internal routinginformation or the additional internal routing information. Fabricmanagement subsystem 704 controls switching fabrics in a networkelement. For example, the fabric management subsystem 704 can place aswitching fabric, such as a switching card or a switching shelf, in anactive mode or in an inactive mode. Content messaging subsystem 705conveys control instructions from the connection management subsystem703 and the fabric management subsystem 704 to other components of anetwork element, for example, line cards and switching fabrics.

FIG. 8 is a block diagram of an egress line card capable of supportingredundant switching fabrics in accordance with an embodiment of theinvention. The egress line card 801 may be a separate line cardproviding an egress path for cells from the switching fabric or merely aportion of a line card providing such an egress path. Egress line card801 includes multiplexer 802, which receives input 804 from a firstswitching fabric and input 805 from a second switching fabric andprovides output 803. A fabric activity input 808 is coupled tomultiplexer 802. Multiplexer 802 normally selects its input betweeninputs 804 and 805 dependent upon a state of fabric activity input 808.However, override mode input 807, which is coupled to multiplexer 802 isused to place multiplexer 802 into an override mode, in whichmultiplexer 802 selects its input according to a state of fabricselection input 806, which is also coupled to multiplexer 802.

FIG. 9 is a block diagram illustrating an ingress line card capable ofsupporting redundant switching fabrics in accordance with an embodimentof the invention. The ingress line card 901 may be a separate line cardproviding an ingress path for cells to the switching fabric or merely aportion of a line card providing such an ingress path. Ingress line card901 includes input 902 and outputs 903 and 904. Ingress line card 901provides network traffic present at input 902 to switching fabricscoupled to outputs 903 and 904, and can do so simultaneously. Thus, bothswitching fabrics can simultaneously remain ready to switch networktraffic.

FIG. 10 is a flow diagram illustrating a method for performing anin-service upgrade of a switching fabric of a network element inaccordance with an embodiment of the invention. In step 1001, which isoptional, new connections are blocked from being established during anupgrade process. By omitting step1001, a method may be performed whichallows new connections to be established during the upgrade process.Such new connections may be accommodated, for example, in accordancewith step 1005, as described below. In step 1002, an internal header isprovided to cells received by the network element. The internal headerhas internal routing information and a predefined field for storingadditional internal routing information. In step 1003, additionalinternal routing information of a connection is inserted in thepredefined field in dependence upon the internal routing information.Step 1003 may include steps 1004 and/or 1005. In step 1004, theadditional internal routing information is inserted for an existingconnection already existing prior to a commencement of an upgradeprocess. In step 1005, the additional internal routing information isincluded in the predefined field for a new connection established aftercommencement of the upgrade process. In step 1006, the switching fabricis upgraded. The upgraded switching fabric is operable to switch a firstplurality of cells onto the connection in dependence upon the additionalinternal routing information. In one embodiment, prior to the upgradingof the switching fabric, the switching fabric is operable to switch asecond plurality of cells on the connection in dependence upon theinternal routing information.

FIG. 11 is a flow diagram of a method for performing an in-serviceupgrade of a switching fabric of a network element in accordance with anembodiment of the invention. In step 1101, an internal header isprovided to cells received by the network element. The internal headerhas internal routing information and a predefined field for storingadditional internal routing information. In step 1102, inclusion of theaddition internal routing information for new connections establishedafter commencement of an upgrade process commences. As an example, acontrol card programs line cards to begin including additional internalrouting information for all cells of all new connections. In oneembodiment, the internal routing information is bit-mapped, for example,designating destinations for cells with bits corresponding to thosedestinations set to a particular value, and the additional internalrouting information is non-bit-mapped, for example, designating aparticular destination for a cell using a plurality of bits rather thana mapping of bits to destinations.

In step 1103, the additional internal routing information is inserted inthe predefined field for all existing connections already existing priorto commencement of the upgrade process. As an example, a control cardprograms line cards to begin including additional internal routinginformation for all cells of all existing connections. In step 1104,while a first switching card is in a non-active mode, the firstswitching card is replaced with a first fabric interface card. In step1105, the first fabric interface card is place in an active mode. When aswitching fabric is in a non-active mode, the network element does notrely on that switching fabric for switching of cells passing through thenetwork element. When a switching fabric is in an active mode, thenetwork element relies on that switching fabric for switching of cellspassing through the network element.

Following step 1105, a decision may be made as to whether or not tocontinue with the upgrade process. For example, if the upgrade processappears to be causing adverse effects on the switching of networktraffic or some other anomalous behavior is noted, a decision may bemade to back out of the upgrade process and revert to the configurationof the network element prior to the commencement of the upgrade process.In the event that it is decided to back out of the upgrade process, thereversion process illustrated in FIG. 12 may be performed. Otherwise,the process continues at step 1106. In step 1106, a second switchingcard is replaced with a second fabric interface card while the secondswitching card is in the non-active mode. In step 1107, the secondfabric interface card is placed in the active mode. In step 1108,inclusion of the internal routing information in the internal header isoptionally discontinued.

In one embodiment, the additional internal routing information isdesignated as having a length greater than that needed to containinformation sufficient to switch a first plurality of cells onto theconnection in dependence upon the additional internal routinginformation. Thus, an excess length of the additional internal routinginformation is available for other information. As an example, thisexcess length may be reserved for future use or used for other purposes,for example, for differentiating a plurality of qualities of service. Inone embodiment, storage of a switching card bit map in a portion of theinternal header used for the internal routing information isdiscontinued. Optionally, the space in the internal header formerlyoccupied by the switching card bit map may be reserved for future use oruse for other purposes. In one embodiment of the method illustrated inFIG. 11, the upgrade process does not result in cells failing to reachtheir destinations. Thus, no data is lost during the upgrade process.Since the network element may remain in service switching cells duringthe upgrade process, the upgrade process may be referred to as anin-service upgrade.

FIG. 12 is a flow diagram illustrating a method for backing out of anupgrade process in accordance with an embodiment of the presentinvention. As noted above, the steps of FIG. 12 may be performedfollowing certain steps of illustrated in FIG. 11, for example,following step 1105. In step 1201, a second switching card is placed inthe active mode. In step 1202, the first fabric interface card isreplaced with the first switching card. From step 1202, the method maycontinue to either of steps 1203 or 1204. In step 1203, inclusion of theadditional internal routing information is discontinued for subsequentnew connections. As an example, a control card programs line cards todiscontinue inclusion of the additional internal routing information forsubsequently established new connections. In step 1204, inclusion of theadditional internal routing information is discontinued for existingconnections and subsequent new connections. As an example, a controlcard programs line cards to discontinue inclusion of the additionalinternal routing information for both existing connections andsubsequently established new connections.

Accordingly, a method and apparatus for performing an in-service upgradeof a switching fabric of a network element has been described. It shouldbe understood that the implementation of other variations andmodifications of the invention in its various aspects will be apparentto those of ordinary skill in the art, and that the invention is notlimited by the specific embodiments described. It is thereforecontemplated to cover by the present invention, any and allmodifications, variations, or equivalents that fall within the spiritand scope of the basic underlying principles disclosed and claimedherein.

1. A method for performing an in-service upgrade of a switching fabricof a network element, the method comprising the steps of: providing aninternal header to cells received by the network element, the internalheader having internal routing information and a predefined field forstoring additional internal routing information; inserting additionalinternal routing information of a connection in the predefined field ofeach cell of the cells in dependence upon the internal routinginformation; and upgrading the switching fabric, the upgraded switchingfabric being operable to switch a first plurality of the cells onto theconnection in dependence upon the additional internal routinginformation, wherein the step of inserting the additional internalrouting information further comprises: inserting the additional internalrouting information for an existing connection already existing prior toa commencement of an upgrade process.
 2. The method of claim 1 wherein,prior to the step of upgrading the switching fabric, the switchingfabric is operable to switch a second plurality of the cells on theconnection in dependence upon the internal routing information.
 3. Themethod of claim 1 wherein the step of inserting the additional internalrouting information further comprises the step of: including theadditional internal routing information for a new connection establishedafter commencement of the upgrade process.
 4. The method of claim 1further comprising the step of: blocking new connections from beingestablished during the upgrade process.
 5. A method for performing anin-service upgrade of a switching fabric of a network element, themethod comprising the steps of: providing an internal header to cellsreceived by the network element, the internal header having internalrouting information and a predefined field for storing additionalinternal routing information; commencing inclusion of the additionalinternal routing information for new connections established aftercommencement of an upgrade process; inserting the additional internalrouting information for all existing connections already existing priorto commencement of the upgrade process; replacing a first switchingcard, while the first switching card is in a non-active mode, with afirst fabric interface card; placing the first fabric interface card inan active mode.
 6. The method of claim 5 further comprising the step of:replacing a second switching card, while the second switching card is inthe non-active mode, with a second fabric interface card.
 7. The methodof claim 6 further comprising the step of: placing the second fabricinterface card in the active mode.
 8. The method of claim 7 furthercomprising the step of: discontinuing inclusion of the internal routinginformation in the internal header.
 9. The method of claim 5 placing asecond switching card in the active mode.
 10. The method of claim 9further comprising the step of: replacing the first fabric interfacecard with the first switching card.
 11. The method of claim 10 furthercomprising the step of: discontinuing inclusion of the additionalinternal routing information for subsequent new connections.
 12. Themethod of claim 10 further comprising the step of: discontinuinginclusion of the additional internal routing information for existingconnections and subsequent new connections.
 13. The method of claim 5wherein the additional internal routing information is designated ashaving a length greater than that needed to contain informationsufficient to switch a first plurality of the cells onto the connectionin dependence upon the additional internal routing information, whereinan excess length of the additional internal routing information isavailable for other information.
 14. The method of claim 5 whereinstorage of a switching card bit map in a portion of the internal headerused for the internal routing information is discontinued.
 15. Themethod of claim 5 wherein the internal routing information is bit-mappedand the additional internal routing information is non-bit-mapped. 16.The method of claim 5 wherein the upgrade process does not result incells failing to reach their destinations.
 17. A switching systemcomprising: at least one line card; at least one switching card, the atleast one switching card coupled to the line card, the at least oneswitching card adapted to be replaceable by fabric interface cards; atleast one control card coupled to the at least one line card and the atleast one switching card, the at least one control card adapted toprogram the at least one line card to insert additional internal routinginformation into a predefined field.
 18. The switching system of claim17 wherein the at least one line card inserts internal routinginformation into a portion of an internal header other than thepredefined field, wherein the internal header includes the predefinedfield.
 19. A switching system comprising: a line card; a fabricinterface card coupled to the line card and to a switching shelf, thefabric interface card and the switching shelf adaptable to replace aswitching card; a control card coupled to the line card, the controlcard adaptable to cause the line card to communicate cells withoutinterruption during replacement of the switching card.
 20. A line cardcomprising: a cell modification circuit for modifying a first cell and asecond cell to include an internal header, the internal header includinginternal routing information and a predefined field for storingadditional internal routing information, wherein the line card isadaptable to be coupled at a first time to a switching fabric, theswitching fabric being operable to switch the first cell in dependenceupon the internal routing information, and to be coupled at a secondtime to an upgraded switching fabric, the upgraded switching fabricbeing operable to switch the second cell in dependence upon theadditional internal routing information.
 21. The line card of claim 20wherein the cell modification circuit inserts the additional internalrouting information into the predefined field of the internal header.22. A control card comprising: a connection management subsystemadaptable to program a line card to modify a cell to include an internalheader, the internal header including internal routing information and apredefined field for storing additional internal routing information;and a fabric management subsystem adaptable to control a first switchingfabric and a second switching fabric, the first switching fabricadaptable to switch the cell in dependence upon the internal routinginformation and the second switching fabric adaptable to switch the cellin dependence upon the additional internal routing information.